1. Field of the Invention
The present invention relates to digital data storage, and more particularly, to techniques for estimating external shock and controlling write operations in a disk drive.
2. Description of the Prior Art
In order to remain competitive, disk drive manufacturers must continually provide increased data storage capacity while rigidly controlling disk drive manufacturing cost. One key to increased storage capacity is increased track density, often expressed as tracks per inch or TPI. Market demand for increased storage capacity has pushed disk drive designers to increase the TPI of disk drives, thereby increasing the likelihood that an external shock event may undesirably force the disk drive""s read/write head over an adjacent track during track following.
Accordingly, there exists a need for a technique that enables a disk drive to minimize the effect of external shock during track following without unnecessarily increasing the disk drive""s manufacturing cost.
The present invention may be embodied in a method for shock estimation and write termination control in a disk drive having a read/write head and a plurality of concentric data tracks on a storage surface of a rotating disk, each data track having data sectors and embedded servo sectors. In the method, the head is positioned over a selected data track of the plurality of concentric data tracks for following the track during a data write operation. The track""s embedded servo sectors are read to generate position error signal values. A write unsafe limit is provided for terminating a data write operation if at least one position error signal value exceeds the write unsafe limit. A shock event limit is provided, and if a current position error signal value is less than the write unsafe limit value, then a function value is calculated based on the current position error signal value and a previous position error signal value. If the calculated function value exceeds the shock event limit, a data write operation is terminated.
In more detailed features of the invention, the calculated function value may be an addition of the current position error signal value and the previous position error signal value, or the calculated function value may be equal to twice the current position error signal value minus the previous position error signal value.
In another embodiment of the invention, a preliminary limit is provided that is smaller than the write unsafe limit. If at least one position error signal value exceeds the preliminary limit without exceeding the write unsafe limit, then a difference limit is provided and a difference is calculated between a current position error signal value and a previous position error signal value. If the calculated difference exceeds the difference limit, a data write operation is terminated.
In another embodiment of the invention, a difference limit and a preliminary limit are provided. The preliminary limit is smaller than the write unsafe limit. A difference is calculated between a current position error signal value and a previous position error signal value. A data write operation is terminated if the current position error signal value exceeds the preliminary limit and the calculated difference exceeds the difference limit.